A hybrid random number generator typically comprises a true random number generator (TRNG) and a cryptographic post processing. The true random number generator exploits a physically unpredictable effect (radioactive decay, thermal noise, jitter in oscillators, etc.) to generate random numbers. Typically, the physical random processes are digitized and a random bit sequence is obtained. This random bit sequence is typically termed raw data sequence. The raw data is typically further subjected to a mathematical post-processing in order to smooth certain technology-related effects, such as a bias, i.e., an imbalance of zeros and ones. The result is a random (bit) sequence that is used for applications (e.g., for the generation of cryptographic keys).
In the case of a hybrid random number generator, a cryptographic post-processing is connected downstream of the true random number generator.